What You Will Learn:

• Understand and define key programming concepts
• Use the JavaScript console
• Understand the console is for testing, does not permanently store code
• Use Arithmetic Operators in console
• Use and concatenate strings in console

Why This is Important:

JavaScript is what gives the web its “magic”. The most useful and interesting applications on the internet today are mostly all powered by JavaScript.

Using the Console

We can play-around with JavaScript in the JavaScript Console. This is like a playground to experiment with JavaScript.

To get to the console, open chrome, and navigate to any webpage. Press command + option + J

This gives you an area down at the bottom of the screen, called the console. The “>” symbol is called the prompt, where you can type JavaScript code.

Simple interpretation

Try typing these lines, pressing enter after each one:

>4
>2+3
>2*3

Note that your friend the interpreter mostly just repeats what you say, but evaluates mathematical expressions. JavaScript performs basic math as you would expect, with the operators ` +, -, /, * .` A less familiar operator is %, or modulo. See if you figure out what modulo does.

> 10 % 5

> 11 % 5

> 13 % 5

> 16 % 5

> 23 % 16

Here are some other mathematical operators:

Strings

So now we know we can do math in the console. The interpreter will do things to pieces of text, too. In programming we call bits of text “strings”.

>"my string"

Note that you have to put text inside quotes before the interpreter can understand them. Anything between quotes is called a string.

Now try adding two strings together:

>"first name" + " last name"

Combining strings with the + operator is called concatenation.

JavaScript uses + symbol for math when it is operating on numbers, but when it sees strings, it will concatenate (link together) the text.

Let’s test this. Try entering these three different expressions:

>1 + 1
>”1” + “1”
>”1” + 1

1 + 1 is a mathematical expression adding two numbers, while “1” + “1” is an expression concatenating two strings of the character 1. If you try to add a string and a number, both pieces are treated as strings and concatenated into a bigger string.

Our code and the results as we use the JS Console are only there until we hit refresh. Think of the console as a place to test ideas quickly, not a place to build something that will endure for the ages.